The present invention relates to detergent tablets, particularly for use in a domestic dishwashing machine.
Detergent compositions are known. While these may be in the form of a liquid or free-flowing solid such as a powder, those in the form of a tablet are now generally available. Known tablets may be of a substantially uniform composition, or may be separated into two or more phases, for example to separate incompatible components from each other, to ensure that different components are released into the wash at different times, or to provide an attractive appearance, especially when the phases have different colours. These tablets may be used, for example, in a washing machine for laundry or a dishwashing machine.
Commercially available tablets are known which have two or more layers of a compressed, granular or powdery composition. A tablet is also known which has an insert or cavity filled with a composition containing a different component from the main phase. For example, we currently sell a dishwashing tablet which is a two-layer tablet containing a third composition in the form of a ball held within a cavity punched in the upper surface of the tablet. The ball has a different colour from the two layers, which provides an attractive appearance. The ball also contains a disrupting agent such that components in the ball are released into the wash before the components of the two layers of the tablet.
The layers of the tablet are formed by compression of particulate material. The cavity is formed by using any appropriately shaped upper punch, having a protrusion corresponding to the shape of the cavity.
The regions beneath and adjacent to the sides of the cavity are compressed to a greater extent than the rest of the tablet, creating an uneven distribution of densities within the tablet. As a consequence, the different portions of the tablet have undesirable different disintegration and solubilisation profiles. If the overall pressure of the upper punch used to form the cavity in the tablet is reduced, there may be an insufficient compression of the shoulders of the tablet. The tablet may then be easily damaged during storage and transport.
Furthermore it is necessary to place accurately the ball in the cavity. If it is not placed exactly in the cavity, the ball tends to disintegrate or break away from the remainder of the tablet. This leads to a high rate of wastage.
We have now discovered a tablet which retains the advantages of this type of tablet, such as an attractive appearance and separation of components into different phases, and which also overcomes the above disadvantages.